A formulation is a mixture of ingredients prepared in a certain way and used for a specific purpose. For example, if you are sick, you may need a formulation of a combination of antibiotics.
If you devise or conceptualize an idea, you can also refer to this act with the noun formulation. If you are a scientist, you may be widely recognized for your skillful formulation of a plan to eradicate a disease. If you are a parent, you may congratulate yourself for the formulation of a plan to get your kids to actually go to bed on time. Of course, the flaw may be that when you conceptualized the plan, you assumed that the kids would cooperate and not want a drink of water every five minutes.